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NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe

NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe

1. Fill in the blanks.

(a) Microorganisms can be seen with the help of a ____________.

(b) Blue green algae fix __________ directly from air and enhance fertility of soil.

(c) Alcohol is produced with the help of __________.

(d) Cholera is caused by __________.

Answer:-

(a) Microorganisms can be seen with the help of a Microscope.

(b) Blue green algae fix Nitrogen directly from air and enhance fertility of soil.

(c) Alcohol is produced with the help of Sugar.

(d) Cholera is caused by Bacteria.

2. Tick the correct answer.

(a) Yeast is used in the production of

(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen

(b) The following is an antibiotic

(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast

(c) Carrier of malaria-causing protozoan is

(i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly

(d) The most common carrier of communicable diseases is

(i) ant (ii) housefly (iii) dragonfly (iv) spider

(e) The bread or idli dough rises because of

(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading

(f) The process of conversion of sugar into alcohol is called

(i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection

Answer:-

  1. a) (ii) alcohol
  2. b) (ii) Streptomycin
  3. c) (i) female Anopheles mosquito
  4. d) (ii) housefly
  5. e) (iii) growth of yeast cells
  6. f) (iii) fermentation

3. Match the organisms in Column A with their action in Column B.

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4. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer:- Microorganisms cannot be seen by the naked eye because they are very small in size. They can be seen by using a microscope only.

5. What are the major groups of microorganisms?

Answer:- Major group of microorganisms are following:-

  1. Bacteria
  2. Fungi
  3. Protozoans
  4. Algae
  5. Viruses

6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer:- Rhizobium and blue green algae

7. Write 10 lines on the usefulness of microorganisms in our lives

Answer:-

  1. Bacteria like Lactobacillus helps in the formation of curd.
  2. Bacteria are also used in the making of cheese.
  3. Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.
  4. Yeast is used in the production of alcohol and wines.
  5. Yeast is also used in the production of bakery products.
  6. Some special microorganisms are used in manufacturing of antibiotics.
  7. Microorganisms act as cleansing agents they decompose the waste products into manure.
  8. Some dead or weakened microbes are used in the making of vaccines.
  9. Rhizobium fix atmospheric nitrogen and help in increasing soil fertility.
  10. Some specific microbes are also used in the biological treatment of sewage.

8. Write a short paragraph on the harmful effects of microorganisms.

Answer:-Microorganism are harmful in many ways. Some of the microorganisms known as pathogens cause diseases in human beings, animals and in plants. Some microbes causes diseases in plants and hence reduces the yield. Some microorganisms that grow on our food sometimes produce toxic substances and cause food poisoning.

9.What are antibiotics? What precautions must be taken while taking antibiotics?

Answer:- The medicines that kill or stop the growth of the disease-causing microorganisms are medicines called antibiotics.

The precautions must be taken while taking antibiotics are following:-

  1. Take it on the advice of a qualified doctors only.
  2. Must finish the course of it as prescribed by the doctor.
  3. Don’t take it unnecessarily.
  4. Take it in the right amount.